Uniformly shaped devices which are capable of swelling when exposed to an aqueous environment have applications in a wide variety of different fields where there is a need to provide temporary or permanent filling or blocking of a lumen, space or void. For example, such devices may be useful in oceanography or plumbing. However, these types of devices are particularly useful for in vivo applications where the shapes of implantable devices and their properties when exposed to in vivo conditions are important. For example, in the field of orthopedics, uniformly shaped devices are useful for implantation into surgically preformed or naturally occurring voids in hard tissue for facilitating bone repair.
Bone repair is necessary to treat a variety of orthopedic conditions. For example, when hard tissue such as bone is damaged as a result of disease or injury, it is often necessary to provide a means for strengthening the damaged bone during the healing process to prevent further damage. This can be achieved externally by placing the area of the body in which the damaged bone is located in a supporting device such as a cast. Alternatively, in the more severe situations where direct support is necessary, the damaged bone can be supported by implanting surgical devices such as metal pins and rods to which the damaged bone is attached while healing.
In many instances, when the bone is severely damaged, or when the damaged tissue necessitates more immediate treatment (i.e. when it is not feasible to wait for the natural healing process to occur), it becomes necessary to increase the integrity and thus the load bearing capacity of the bone itself by using implants that are placed within the tissue. Such implants may take the form of plugs or rods, which are placed in the hard tissue after forming a depression or channel therein.
In other instances, tissue damage results in the dissociation of two or more tissues, most often a soft tissue such as tendon or ligament which detaches from bone. In such situations, it is necessary to reattach the tissues together either permanently, or temporarily while the two tissues became permanently reattached during the healing process. Devices for reattaching tissues have been described in the literature. For example, Innovasive Devices, Inc. (Marlborough, Mass.) markets a device called the ROC.TM. Fastener which is a nonresorbable, permanent synthetic insert. Other synthetic devices include the following: metal barbed anchors which are designed to hold a suture (Mitek, Norwood, Mass.); metal screws to which suture material can be attached (Linvatec, Largo, Fla.); and plastic suture anchors with expandable wings (Acufex Microsurgical, Inc., Norwood, Mass.).
Unlike the synthetic permanent implants heretofore described, some manufacturers have recently described the use of hydrolizable inserts. For example, the Suretac.TM. implant (Acufex Microsurgical, Inc., Norwood, Mass.) is described as an absorbable tack of a synthetic polyglyconate copolymer. (Arthroscopy 11(2):194-198 (1995).) Additionally, European Patent No. 0412280 describes a pin made of poly (L-DL-lactide). However, neither of these devices is both resorbable and swellable.
The implant body which comprises the principle component of the implant device of the present invention is preferably formed from a dehydrated crosslinked collagen matrix. Collagen matrices have been previously described for various uses. See, for example: U.S. Pat. Nos. 5,162,430; 5,324,775; 5,328,955; 5,475,052; 5,523,348; 5,304,595; 5,306,500; 5,376,375; 5,413,791; and 5,446,091. In the field of tissue treatment, collagen-containing materials have been described for use in soft tissue repair (U.S. Pat. Nos. 4,424,208 and 4,582,640.) As described therein, these materials were used in the form of injectable aqueous dispersions of collagen gels.
Additionally, U.S. Pat. Nos. 4,563,350 and 4,888,366 describe the use of lyophilized ('350) and preformed ('366) collagen carriers of osteoinductive factors in bone repair. When used as preformed solid implants, these carriers consist generally of ceramic materials which are held together by collagen. Similarly, U.S. Pat. No. 4,776,890 describes non-crosslinked collagen/mineral implants, which can be moistened and molded into a desired shape before implantation. Therein, crosslinking is described as being undesirable because of its inhibitory effects on bone ingrowth. Also, U.S. Pat. Nos. 4,795,467, 5,035,715 and 5,110,604 describe porous collagen-containing implants for use in bone repair and/or wound healing.
Uniformly shaped swellable devices made from polymeric materials are not easily manufactured. This is due in part to the fact that in order to be swellable, it is generally necessary for the polymeric material to be preformed while "wet," then dried to effect shrinkage. When the material is rewetted, it will thus have a tendency to swell in size. However, the drying process is not easily controlled and often results in formation of irregularly and irreproducibly shaped materials. Accordingly, there is a need to provide methods and apparatuses for making swellable, uniformly shaped devices from polymeric materials. The present invention therefore relates to methods and apparatuses for making such devices using extrusion molding, and more particularly to collagen-containing devices which, when dried, have uniform shape, and have predetermined swelling characteristics.
Shaped collagen-containing products and methods of making shaped collagen-containing products are known. Common methods for fabricating shaped collagen include film-forming methods, such as the casting of a lenticular device defined by a mold as disclosed in U.S. Pat. No. 5,322,648. In addition, U.S. Pat. No. 5,501,706 discloses a shaped medical implant structure which is shaped using a containment member. Extrusion is also used to form shaped collagen products. For example, U.S. Pat. No. 4,923,380 discloses a method for extruding a reactive collagen gel through a spinneret into a coagulating bath to create a collagen tubule suitable for prosthetic and nerve-suture applications. A shaped product is also formed by extruding a collagen-containing precursor mixture into a coagulating solution and subsequently freezing to achieve the final shaped collagen product as disclosed by U.S. Pat No. 4,533,358.
Although the aforementioned patents and publications address to some extent how to produce shaped collagen-containing products for medical purposes, there exists a need for improved methods of producing dried, swellable, uniformly shaped collagen-containing products which do not require processing steps that are expensive or involve numerous solvent treatments.
The present invention relates to the use of dense, preformed hard tissue implants comprising a crosslinked implant body which is both resorbable (i.e. it is replaced by ingrowth of tissue) and swellable. Because the implant body swells after insertion, the implant becomes anchored in place, which eliminates the necessity for anchoring structures such as barbs, fins and wings. Additionally, because the implant body is dense when implanted and thereafter rendered less dense by degradation, it can initially provide adequate mechanical integrity while later serving as a scaffold for tissue ingrowth.
The implants of the present invention are placed within the hard tissue to increase its load bearing capacity, and/or to serve as a site for attachment of a second tissue. Also, by combining the use of these implants with other surgical devices such as sutures, screws, pins and rods, the effectiveness of tissue repair can be greatly enhanced.
The present invention also relates to apparatuses and methods for manufacturing implants, as well as polymer devices which are suitable for use in non-medical applications which, like the implants, are uniformly shaped and swellable.